A power supply system (e.g., an adaptor) is used to convert the alternating current (ac) voltage from the utility companies into a direct current (dc) voltage suitable for electronic devices. In many applications, the power supply system is required to operate with a wide input voltage range. For example, in China and many European countries, the ac supply voltage from the utility companies is in a range from about 210 V to about 240 V and has a frequency of about 50 Hz. The voltage above is an RMS voltage. RMS stands for Root Mean Square. In North America, the ac supply voltage is in a range from about 100 V to about 120 V and has a frequency of about 60 Hz. Electronic devices such as a laptop computer may need a universal adapter so that the laptop computer can work in different countries.
The power supply system (e.g., an adaptor) usually includes an ac/dc stage (e.g., a rectifier) and an isolated dc/dc stage (e.g., an isolated dc/dc converter). The ac/dc stage converts the power from the ac utility line and establishes a dc bus for the isolated dc/dc stage. The ac/dc stage may comprise a variety of electromagnetic interference (EMI) filters and a bridge rectifier formed by four diodes. The EMI filters are employed to attenuate both differential mode noise and common mode noise. The bridge rectifier converts the ac voltage into a full-wave rectified dc voltage. Such a full-wave rectified dc voltage provides a steady dc input voltage for the isolated dc/dc stage through a plurality of smoothing capacitors coupled to the output of the bridge rectifier.
The isolated dc/dc stage converts the voltage of the dc bus to a voltage suitable to electronics loads such as tablets, printers, mobile phones, personal computers, any combinations thereof and the like. The isolated dc/dc stage can be implemented by using different power topologies, such as flyback converters, forward converters, half bridge converters, full bridge converters and the like.